This application claims the priority of German application 198 19 712.8, filed May 2, 1998 in Germany, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a control cylinder for a steering system of a motor vehicle, with a cylinder housing in which a piston part secured to a piston rod is mounted linearly displaceably, said part dividing a cylinder chamber within the cylinder housing into working chambers located axially opposite one another, said chambers being filled completely with damping medium. The piston part has at least one through-flow cross section connecting the working chambers with one another, said cross section being sealable by sealing means.
A control cylinder of this kind is known from European Patent Document No. EP 0 424 629 B1 (corresponding to U.S. Pat. No. 5,113,716) for a steering column arrangement of a motor vehicle. The known steering column arrangement has two jacket tube parts displaceable telescopewise with respect to one another, with a hydraulic cylinder mounted axially parallel being provided for displacement. One end of the hydraulic cylinder is mounted permanently on the vehicle. The other end is fastened to the displaceable jacket tube part so that actuation of the hydraulic cylinder causes displacement of one jacket tube part relative to the other jacket tube part. A disk-shaped piston part is provided in the hydraulic cylinder, said part being secured to an axially displaceable piston rod. The piston part divides a cylinder chamber on the hydraulic cylinder into two working chambers filled completely with hydraulic oil. A through-flow bore is provided in the piston part, said bore connecting the two working chambers with one another. The through-flow bore can be closed by a switchable valve that serves as sealing means.
A goal of the invention is to provide a control cylinder of the type recited at the outset that provides improved occupant protection for a driver of the motor vehicle when the control cylinder is used in a steering column arrangement.
This goal is achieved according to preferred embodiments of the invention by virtue of the fact that at least one flexible sealing lip is provided as sealing means, said lip exposing the through-flow cross section in its unloaded resting position, said lip being deformable, upon an abrupt relative movement, by the level of an impact load into a closed position that seals off the through-flow cross section at least to a large extent. The resistance to deformation of the (at least one) sealing lip is chosen so that during normal control processes the sealing lip remains in its resting position between the piston rod and the cylinder housing. Hydraulic oil in particular is provided as the damping medium in the device according to the invention. The use at least largely of the incompressible damping medium is advantageous for the solution according to the invention.
As a result of the solution according to the invention, when a vehicle collision occurs, a relative movement between the piston part and the cylinder housing and hence a relative movement between a jacket tube part and the vehicle body is necessarily avoided. When an impact load is imposed from the steering wheel side on the steering column arrangement, displacement of the steering wheel into the cockpit area is avoided so that the steering wheel offers a reliable support for deploying an airbag. When the impact load is imposed in the opposite direction by the steering gear, the steering wheel is reliably prevented from being pushed into the vehicle interior and there leading to the risk of injury to the driver.
With the solution according to the invention, in which the control cylinder is designed as a damping cylinder, improved occupant protection is thus achieved. The at least one flexible sealing lip offers an especially simple solution for blocking corresponding adjusting movements of the control cylinder without external switching devices being required for the purpose.
In certain preferred embodiments of the invention, both of the end openings located opposite one another of the (at least one) through-flow cross section are each provided with at least one sealing lip. The opposite sealing lips are alternatively deformable into their closing positions under opposite axial loads. As a result, assurance is provided that the control cylinder can perform its blocking function in both opposite axial directions, so that the corresponding steering column part can be locked integrally with the vehicle under loads coming from the steering wheel and also from the opposite direction, namely from the direction of the steering gear.
In certain preferred embodiments of the invention, a remaining through-flow cross section that cannot be closed is provided which is much smaller than the closable through-flow cross section. As a result, impact energy can be reduced in the control cylinder and can simultaneously reduce a maximum load producing a maximum effect on the driver.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.